1. Field of the Invention
The present invention relates to a lead frame, and a method for producing a semiconductor device and a method for inspecting the electrical properties of a small device using the lead frame.
2. Background Art
Resin-sealed semiconductor devices using a lead frame are widely used as inexpensive small-pin IC packages, whose pin counts and package sizes vary greatly.
FIG. 9 is a perspective plan view of a device employing a conventional SOP (Small Outline Package) type package, the view showing how the IC chip is mounted on the lead frame and molded with resin. In the figure, reference numeral 22 denotes a package made up of a semiconductor chip molded with resin, and 23 denotes a lead frame having the package 22 mounted thereon forming a single unit. The lead frame 23 includes a die pad 24, leads 25, suspension leads 26, and tie bars 27. A semiconductor chip 28 is bonded onto the die pad 24 by means of die bonding. The leads 25 include inner leads 25a disposed within the package and outer leads 25b extending from the inner leads 25a to the outside of the package. The inner leads 25a are connected to electrode pads 29 on the semiconductor chip 28 through wires 30. On the other hand, the ends of the outer leads 25b extending from the inner leads 25a are connected to a framework 31. Furthermore, the suspension leads 26 are provided between the semiconductor chip 28 and the framework 31 such that they intersect the outer leads 25b and thereby function to, when the package 22 is molded with resin, prevent the resin from flowing to the outer leads 25b. The suspension leads 26 extend in parallel with the longitudinal direction of the die pad 24, and both of their ends are connected to the framework 31 so that the suspension leads 26 function to support the die pad 24.
Description will be made below of a method for manufacturing a semiconductor device using the lead frame shown in FIG. 9. First of all, the semiconductor chip 28 is mounted on the die pad 24 and connected to the inner leads 25a through the wires 30 using the wire bonding method. Subsequently, the die pad 24, the inner leads 25a, the semiconductor chip 28, and the wires 30 are sealed with resin using the transfer molding method to form the package 22. The actual lead frame has a structure in which, for example, a plurality of devices 32 are disposed alongside of one another in the longitudinal direction of a lead frame 33, as shown in FIG. 10. Each device 32 is arranged such that the longitudinal direction of outer leads 34 and that of the lead frame 33 are in parallel with each other. Then, in FIG. 9, the tie bars 27 and the tip of the outer leads 25b, and the suspension leads 26 are cut, and the outer leads 25b are bent in a predetermined shape, completing a resin-sealed semiconductor device. FIG. 11(a) is a plane view of a completed resin-sealed semiconductor device, while FIG. 11(b) is a side view.
Conventionally, the electrical properties of each individual semiconductor device cut off as described above is inspected independently by connecting an electrode terminal to each lead. However, this means that it is necessary to set each semiconductor device at a predetermined inspection position for measurement one at a time, which requires considerable time. In addition, since each semiconductor device is small and therefore difficult to handle, JAM is likely to occur due to dropping at the time of inspection or transfer of the device. Furthermore, it is necessary to prepare an inspecting aid(s) for each package size, incurring a cost.
The present invention has been devised in view of the above problems. It is, therefore, an object of the present invention to provide a lead frame with which electrical property inspection (of a each device) can be efficiently carried out, and a method for manufacturing a semiconductor device using the lead frame.
Another object of the present invention is to provide a method for efficiently inspecting the electrical properties of a small device.
Other objects and advantages of the present invention will become apparent from the following description.
According to one aspect of the present invention, a lead frame comprises a plurality of framework assemblies. Each framework assembly includes a framework, a suspension lead whose both ends are connected to said framework, a die pad which is supported by the suspension lead and on which a semiconductor chip is mounted, a plurality of inner leads whose front ends are connected to electrodes on the semiconductor chip through wires, a plurality of outer leads extending from back ends of the plurality of inner leads toward outside of the semiconductor chip, wherein front ends of the plurality of outer leads are connected to no other portions and leave in a free state, a first tie bar located near the plurality of inner leads across the plurality of outer leads, wherein both ends of the first tie bar are connected to the framework, a second tie bar located near the front ends of the plurality outer leads across the plurality of outer leads, wherein both ends of the second tie bar are connected to the framework, and a lead support protruding from the framework""s surface facing to the front ends of the plurality of outer leads to the front ends of them and having a rectangular shape whose long sides are in parallel with a direction in which the plurality of outer leads are disposed alongside of one another and whose length is approximately equal to a length of space occupied by all of the plurality of outer leads. The plurality of framework assemblies are disposed alongside of one another in a direction perpendicular to a direction in which the plurality of outer leads extend. A distance between close-set outer leads of each two neighboring frameworks is substantially n times a pitch of the plurality of outer leads of each framework, wherein n is an integer.
According to another aspect of the present invention, in a method for manufacturing a semiconductor device, a lead frame is prepared. The lead frame comprises a plurality of framework assemblies. Each framework assembly includes a framework, a suspension lead whose both ends are connected to the framework, a die pad which is supported by the suspension lead and on which a semiconductor chip is mounted, a plurality of inner leads whose front ends are connected to electrodes on the semiconductor chip through wires, a plurality of outer leads extending from back ends of the plurality of inner leads toward outside of the semiconductor chip, wherein front ends of the plurality of outer leads are connected to no other portions and leave in a free state, a first tie bar located near the plurality of inner leads across the plurality of outer leads, wherein both ends of the first tie bar are connected to the framework, a second tie bar located near the front ends of the plurality outer leads across the plurality of outer leads, wherein both ends of the second tie bar are connected to the framework; and a lead support protruding from the framework""s surface facing to the front ends of the plurality of outer leads to the front ends of them and having a rectangular shape whose long sides are in parallel with a direction in which the plurality of outer leads are disposed alongside of one another and whose length is approximately equal to a length of space occupied by all of the plurality of outer leads. The plurality of framework assemblies are disposed alongside of one another in a direction perpendicular to a direction in which the plurality of outer leads extend. A distance between close-set outer leads of each two neighboring frameworks is substantially n times a pitch of the plurality of outer leads of each framework, wherein n is an integer. Then, in the method for manufacturing the semiconductor device, the semiconductor chip is mounted on the die pad. Between the electrodes on the semiconductor chip and the plurality of inner leads through the wires are electrically connected. The semiconductor chip, the die pad, the wires, and the plurality of inner leads are sealed with resin to form a small device. The front ends of the plurality of outer leads and the lead support are sealed with resin. The first tie bar and the second tie bar are cut to electrically isolate each of the plurality of outer leads. An inspecting aid having a plurality of electrode terminals disposed alongside of one another at a pitch substantially 1/m times a pitch of the plurality of outer leads of each framework is used (where m is an integer). And the plurality of electrode terminals are connected to the plurality of outer leads to inspect electrical properties of the small device. The suspension lead is cut off. The lead support is separated from each framework. The plurality of outer leads are processed. The lead support is cut off.
According to other aspect of the present invention, in a method for inspecting electrical properties of a plurality of small devices which are formed by mounting a plurality of semiconductor chips on a common lead frame, connecting a plurality of leads to each semiconductor chip, and then sealing each semiconductor chip with resin; a inspecting aid having a plurality of electrode terminals disposed at equal intervals is disposed, such that a direction in which the plurality of leads are disposed alongside of one another is parallel to that in which said plurality of electrode terminals are disposed alongside of one another. The plurality of electrode terminals are connected to the plurality of leads, wherein the plurality of leads are disposed at a pitch substantially n times a pitch of the plurality of electrode terminals (where n is an integer).
Other and further objects, features and advantages of the invention will appear more fully from the following description.